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HSS, AHSS and aluminum jockey for position in the race to cut auto curb weight

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High-strength steel (HSS) and aluminum applications in auto body designs have reached all-time highs, with increasingly strict government regulations driving the need for better fuel economy and lower carbon dioxide emissions—and further gains are anticipated, including in mixed applications.

The decline in curb weight from 2004 to 2009 was the largest in nearly 30 years, according to a recent study by Troy, Mich.-based Ducker Worldwide LLC. Over the past two years alone, an average of more than 114 pounds of mild-strength steel was replaced in each new vehicle by HSS and aluminum and through a shift to different body structures.

"There's not one car company that we've come across that doesn't make use of increasing amounts of high-strength steel," said Ron Krupitzer, vice president of automotive applications for the American Iron and Steel Institute's Steel Market Development Institute.

Advanced high-strength steels (AHSS) now account for nearly 15 percent of all steel in new vehicles compared with 10 percent in 2007, making it the fastest-growing automotive material, according to the AISI.

Krupitzer noted that flat-rolled and other steel products still accounted for more than half the curb weight of 2009 vehicles. "Steel is not only the existing material in a vehicle, but it could very well be transformed to the new products that have completely different performance standards," he added.

For instance, the family of AHSS that the auto industry uses has gone from a 600-megapascal (MPa) tensile strength level to 1,000 MPa, according to Roger Heimbuch, executive director of the Southfield, Mich.-based Auto/Steel Partnership. And the associated cost is minimal because less material is required as automakers develop smaller vehicles, he said.

New HSS products represent "the fastest-growing material in the car, by far, because it is a cost-effective solution to mass reduction," Heimbuch said, adding that a new generation of AHSS will be coming to market within the next couple of years.

Heimbuch noted that the so-called body-in-white part of vehicle assembly—the stage in which the car body sheet metal is assembled—still focuses on traditional steel use. "It's the hang-on components—doors, deck lids—that have been the parts that have swung between materials," he said.

Meanwhile, aluminum continues to see greater market share in vehicles. Aluminum accounted for an all-time high of 8.6 percent of average curb weight in 2009 vehicles, according to the Council for Automotive Research, with more of the material being used in hoods, engine blocks, control arms and suspension links. Less aluminum was used in crossmembers—a structural section of steel that is bolted across the underside of a unibody motor vehicle—and in cradles, replaced by HSS in some applications.

"Given the regulations that are being put in place all around the world, aluminum is entering a golden age in automotive," said Randall Scheps, marketing director at Pittsburgh-based Alcoa Inc., pointing out that in addition to hoods and deck lids, aluminum is on the cusp of high-volume applications in door and roof panels.

Alcoa is heavily involved in the auto industry, supplying everything from aluminum wheels for Detroit-based General Motors Co.'s much-anticipated Chevrolet Volt electric car to lightweight door assemblies for the Nissan GT-R sports sedan. In the case of the GT-R, aluminum provides a weight savings of 30 to 35 percent, he said.

"We are really starting to hit the limit in how much weight can be saved with a steel body design and I think the very next logical step is aluminum," Scheps said. "We are seeing auto executives all over the world coming to the realization that aluminum is going to be the only way to get there."

Scheps pointed to a Ducker Worldwide report that predicts aluminum content in North American vehicles will be greater than 10 percent, or 376 pounds, of the anticipated 3,500-pound curb weight by 2020, while worldwide aluminum content is expected to grow to about 300 pounds per vehicle by 2020.

"We have never seen such a driving force in new projects and applications as lightweighting in the market," said Laurent Castor, general manager of automotive structures for Europe at Alcan Automotive Structures, a division of Rio Tinto Alcan. The company is a world leader in providing aluminum crash-management systems, cockpit carriers and body-in-white structures for the automotive industry.

Castor notices two significant trends when it comes to aluminum content in vehicles: More high-end automakers who are already leaders in aluminum use, like Germany's Audi AG, are aggressively searching out new applications, even considering all-aluminum vehicles; and aluminum is making significant strides at all major automakers in areas of the vehicle where it previously had only limited exposure, such as in bumpers, crash-management systems, cockpit carriers and suspension parts.

"Before, for example, aluminum crash-management systems might be limited to a medium-sized car. Now, next-generation small cars are getting the same treatment," Castor said. "We have never seen such a move with such a dimension."

One of the biggest changes steel and aluminum producers expect to face is the global auto industry's shift away from full-frame large trucks and sport utility vehicles to lighter unibody vehicle segments. In unibody designs, the floor, roof and panels are welded together into one unit, thereby eliminating the need for a separate frame. This helps to reduce weight and improve fuel economy.

In North America, 77 percent of vehicles manufactured in 2009 used unibody frames, and this is expected to rise to more than 80 percent by 2014, according to CSM Worldwide Inc.

For aluminum producers, this presents new challenges but also added opportunities. While aluminum accounted for 8.6 percent of average vehicle curb weight in 2009, it made up only 1 percent, or less than 8 pounds, of unibody structures. A Ducker Worldwide study expects that to increase to 4 percent, or 26 pounds, by 2020, while HSS grades are expected to account for more than 50 percent of light vehicles with unibody architecture.

"Aluminum is still very young in the auto industry, and we're only now starting to see second-generation aluminum alloys for automotive applications," said Castor, who also expects to see an increase in mixed applications of aluminum and steel. "The idea is always to find the right design for the right material." DARCY KEITH

Jamie Zachary contributed to this story.

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